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Forces in a nucleus/atom

Discussion in 'MCAT Study Question Q&A' started by SereneAurora, Aug 1, 2011.

  1. SereneAurora

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    What types of forces are present in an atom? This question always confuses me cause the answer choices are always a combination of the following:
    Gravitational ( this one confuses me: e have too small of a mass to be effected by this force right?)
    Electrical (yes)
    Centripetal (yes????)
    Electromagnetic (yes)


    Thanks
     
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  3. collegestud2013

    collegestud2013 Probationary Status
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    There are only 4 forces in the universe...

    Gravity: almost negligible at the atomic level
    Electromagnetism: from the charges of the protons and neutrons
    Strong force: holds the protons in the nucleus together
    weak force: causes radioactive decay
     
  4. SereneAurora

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    So how do the e remain in orbit since gravitational force is negligible?
     
  5. circulus vitios

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    Electrons don't actually orbit a nucleus in the classical sense.

    Here's a simple explanation on why negative electrons and the positive nucleus don't attract one another: http://www.physicsforums.com/showpost.php?p=3046518&postcount=2
     
  6. notbobtrustme

    notbobtrustme Crux Terminatus
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    orbitals are quantized. they don't orbit the nucleus like a planet orbits the sun.
     
  7. MD Odyssey

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    This is a very fundamental concept to organic and inorganic chemistry. The fact that you aren't clear on it means you need to go back to your textbook and read through sections on the quantum-mechanical picture of the atom.

    In general, electrons in atoms do not have well-defined positions and momenta as one would expect classically - to do so would violate the Heisenberg uncertainty principle. Instead, we describe the state of the electron as being confined to an orbital, which is really a region in space where the probability of finding the electron is some constant, usually 90%. It turns out that, for a a single electron system, such as hydrogen, we can actually solve the Schrodinger equation which tells us what those probability functions would be and what energies they have associated with them. This gives rise to the familiar s, p, d, and f orbitals you've seen before.

    For atoms with more than one electron, we can't actually solve the equation to get the probability functions because of, among other things, electron-electron repulsion. So, we make the approximation that the electrons don't interact at all and then use the probability functions we had for hydrogen. This allows us to, in some way, describe what's going on in atoms. The complete picture is actually quite a bit different and of course, the orbital picture changes considerably when we start talking about molecules and bonding.

    For anyone reading this, understand that I've purposefully left out a lot of things and am being somewhat misleading about the probability functions. In reality, the solutions to the Schrodinger equation define the states of the electron, the so-called eigenvectors or stationary states of the electron, and the allowable energies for each state. The probability functions which are plotted in chemistry textbooks are usually the square of the wavefunction. None of this is all that important, but I wanted to be precise for posterity.
     
  8. MT Headed

    MT Headed snow, PBR, and bears
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    For the purposes of the MCAT, wouldn't it suffice to say that the reason the electrons hover near the nucleus is because the nucleus has a positive charge and the electron has a negative charge?

    Electromagnetic force is one of the 4 forces mentioned in post #2.
     
  9. MD Odyssey

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    No. You really do need understand the basics idea of atomic orbitals. A lot of other concepts depend upon it - examples are things like aromaticity, resonance, and hyperconjugation, among others.
     

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